At present days, patients who suffer from skin diseases due to skin barrier dysfunction, such as a high incidence of atopic dermatitis, have increased rapidly. This is considered to be caused by an excessive increase in stress (see, for example, Patent Documents 1, 2, 3, and 4). In fact, there is a high incidence of the skin barrier dysfunction, so it is required to develop means for preventing a disease in an early stage from becoming severe or means for ameliorating an actual symptom.
However, in many cases, expression of the skin barrier dysfunction described above is liable to be recognized after developments of severe symptoms such as an occurrence of skin roughness and a rapid increase in amount of transepidermal water loss. Accordingly, it can be said that the development of means for detecting such skin barrier dysfunction in an early stage has been desired.
There are some proposals on animal models for skin barrier dysfunction (see, for example, Patent Documents 5 and 6), but in all the proposals, animals must be used and much time and efforts are required. Further, there is a room for doubt about its reproducibility. Moreover, in such screening using animal models, the number of test samples to be evaluated is limited.
There has not been known at all a method of evaluating skin barrier function using culture cells.
Meanwhile, there has been known that a calcium ion is involved in differentiation/maturation of epidermal/horny layer cells, and that presence of an appropriate amount of the calcium ion gives order to differentiation/maturation of epidermal/horny layer cells. Also, there has been known that an appropriate concentration gradient of the calcium ion from a lower layer of an epidermis toward an upper layer thereof provides a function of constructing a sufficient barrier structure. However, there has been also known that the excessive calcium ion impairs the skin barrier function (see, for example, Non-patent Documents 1, 2, and 3). Moreover, a technology for adjusting the concentration of a metal ion such as a calcium ion in the skin has not been known at all.
[Patent Citation 1] JP 2002-291909 A
[Patent Citation 2] JP 2000-159666 A
[Patent Citation 3] JP 2000-035425 A
[Patent Citation 4] JP 10-279505 A
[Patent Citation 5] JP 2001-321016 A
[Patent Citation 6] WO 2003/053466
[Non Patent Citation 1] Hwang J. et al, J Biol. Chem., (2007), in print
[Non Patent Citation 2] Ahn B K. et al, Arch Dermatol Res., 2007; 299(2): 53-7
[Non Patent Citation 3] Yuki T. et al, Experimental Dermatology, 2007; 16(4), 324-330